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采用落管技术实现了Ni-39.3％Mo和Ni-45％Mo亚共晶合金与Ni-47.7％Mo共晶合金在不同过冷条件下的无容器快速凝固.Ni-39.3％Mo合金在深过冷条件下形成了初生Ni枝晶和共晶组织.随着过冷度的增加.Ni枝晶发生组织细化,枝晶间的间距Lg显著减小.Ni-45％Mo亚共晶合金中的初生Ni枝晶,随着过冷度的增大由粗大的枝晶向等轴晶转变.当过冷度小于43 K时,液滴中形成许多碎断的Ni枝晶.当过冷度在43-113K之间时,凝固时间小于枝晶熔断时间,Ni枝晶不再发生熔断,形成呈辐射状的粗大枝晶.当过冷度大于113 K时,液滴中形成等轴晶,Ni固溶体与NiMo金属问化合物两相分离生长.Ni-47.7％Mo共晶合金凝固组织随着过冷度的增加由层片共晶组织向不规则共晶组织转变.理论分析表明,深过冷Ni-39.3％Mo,Ni-45％Mo和Ni-47.7％Mo熔体中,Ni枝晶的生长随着过冷度的变化发生了溶质扩散控制生长向热扩散控制生长的转变,发生转变所需的过冷度△Tct分别为66.6,81.9和85.0 K.随着合金中Ni含量的增高,Ni枝晶的生长发生动力学转变所需的温度Tct逐渐降低.
The tube-free rapid solidification of Ni-39.3% Mo and Ni-45% Mo hypoeutectic alloy and Ni-47.7% Mo eutectic alloy under different supercooling conditions was achieved by drop tube technology. Under the supercooling conditions, primary Ni dendrites and eutectic structures were formed. With the increase of undercooling, the microstructure of Ni dendrite was refined and the interlamellar spacing Lg was significantly reduced.Ni-45% Mo hypoeutectic alloy In the primary Ni dendrite, with the increase of undercooling from coarse dendrite to equiaxed crystal when the undercooling is less than 43 K, the droplets formed in a number of broken Ni dendrites.When the overcooling Degree between 43-113K, the solidification time is less than the dendrite fusing time, Ni dendrite no longer fuse, the formation of radial coarse dendrites. When the undercooling is greater than 113 K, the droplets form equiaxed , The Ni solid solution and the NiMo metal intermetallic compound are separated and grown in two phases.The solidification microstructure of Ni-47.7% Mo eutectic alloy changes from lamellar eutectic to irregular eutectic with the increase of undercooling.The theoretical analysis shows that the solidification microstructure of Ni-47.7% In cold Ni-39.3% Mo, Ni-45% Mo and Ni-47.7% Mo melts, the growth of Ni dendrites undergoes solute diffusion as the undercooling changes. Transformation, the desired occurrence of transition subcooling △ Tct respectively 66.6,81.9 and 85.0 K. As the increase of Ni content in the alloy, Ni dendrite growth occurs kinetics desired transition temperature Tct decreased.